1. Field of the Invention
The invention relates generally to a transmission lockout device and, more particularly, to a removable overdrive lockout device for a range shift type vehicle transmission.
2. Summary of Related Art
Vehicle transmissions, especially those intended for use in heavy equipment, such as trucks and tractors, often include plural multiple gear selecting devices which are mechanically connected. For example, a five forward speed main gear reduction section may be combined with a two speed range gear reduction section providing a low range and a high range. The resulting combination provides ten forward speeds or gear ratios.
In such transmissions, generally known as range shift type transmissions, it is frequently necessary to prevent operation of the transmission in a given combination of gear ratios due to intrinsic design or extrinsic application considerations. It thus may be necessary to positively preclude shifting such a transmission into certain combinations of gear ratios. For example, in a transmission having five forward gear ratios supplemented by a high/low range selection feature, it may be desirable to prevent simultaneous engagement of the fifth gear of the main section and the high range of the range section. This is especially so where the transmission includes a 10th gear overdrive. Any means which will prohibit such a given selection must, of course, not effect the selection of any other gear ratio.
Lockout devices which perform a similar function have been utilized previously on splitter type transmissions. Such lockout devices are comprised of an auxiliary shift rail and lockout pin which mechanically inhibit selection of certain gear ratio combinations. These devices are totally enclosed within the transmission housing and can not be removed or rendered inoperable without disassembling the entire transmission. This is disadvantageous in that original purchasers of trucks typically desire a direct drive transmission to keep highway speeds down and thereby increase economy. On the other hand, many second owners appear to value performance above economy and, therefore, would prefer a truck having a transmission provided with a 10th gear overdrive. Should the original owner desire to remove or render inoperable such a lockout device to increase the resale value of the truck, it would be necessary to disassemble the transmission and remove the lockout device.